Hydraulic Drive for Cryogenic Fuel Pump

ABSTRACT

A system for delivering cryogenic fuels to an engine uses a plurality of cryogenic pumps operating in offset phases to deliver high pressure fuel with a minimum of pressure ripple. The cryogenic pumps use engine oil and a hydraulic pump for actuation via electrohydraulic valves. A charge pump maintains pressure in the feed line so that the cryogenic pumps can be located away from the cryogenic fuel tank. A control strategy for the hydraulic pumps allows output pressure and flow rate to be closely controlled and regulated.

TECHNICAL FIELD

The present disclosure relates to fuel delivery systems for engines and more particularly to a hydraulic drive for pumping cryogenic liquid fuels.

BACKGROUND

Many industries including transportation, construction, mining and others are turning to the use of liquefied natural gas (LNG), liquid propane, and other fuels that are gases at room temperature or pressure. These fuels are economically viable and much cleaner burning alternatives to gasoline and diesel. In order to optimize storage and transport, these fuels are kept at cryogenic temperatures, that is, temperatures low enough to keep the gaseous-at-room temperature fuels in a liquid state.

Cryogenic fuel delivery systems have many challenges. One is that in order to keep the fuel in the liquid state until it reaches a vaporizer at the engine the fuel must be kept at high pressure after it leaves the cryogenic storage tank, so that current systems mount the fuel pump at or even inside the cryogenic storage tank. Another is that the crank and crosshead drives that run off the engine to pump the fuel are limited by the minimum crank speed of the engine and minimum flow or turn-down ratio of the pump. Further, these crank and crosshead drives require their own oil lubrication systems separate from the normal engine lubrication system. Because the crank and crosshead drives are necessarily near the engine, some applications with physical space limitations are not able to locate the fuel tank close enough to the engine to maintain the required pressure in the fuel after leaving the fuel tank, for example, in locomotives.

U.S. Pat. No. 6,898,940 ('940) teaches using a hydraulic pump located at the cryogenic fuel tank to pump LNG to an engine. The '940 patent teaches co-location of a single pump with the cryogenic fuel tank and also requires a separate hydraulic system for powering the pump. The '940 patent fails to disclose a plurality of hydraulic pumps that use engine oil as their hydraulic fluid. The '940 patent also fails to disclose feed pump in a feed line between the cryogenic tank and the pump so that the pump can be located away from the cryogenic tank.

SUMMARY OF THE DISCLOSURE

In one aspect of the disclosure a system for delivering cryogenic fuel from a cryogenic fuel tank to an engine has a plurality of hydraulically operated cryogenic pumps coupled to the cryogenic tank and a plurality of electrohydraulic valves, each coupled to one respective cryogenic pump. Each of the plurality of electrohydraulic valves is configured to selectively supply or drain hydraulic fluid to its respective cryogenic pump. The system also includes a controller coupled to each of the plurality of electrohydraulic valves. The controller is configured to activate each of the plurality of electrohydraulic valves in a sequence according to a fuel requirement of the engine.

In another aspect of the disclosure, a method of delivering cryogenic fuel from a cryogenic tank to an engine includes providing a plurality of cryogenic pumps. Each cryogenic pump has a hydraulic chamber coupled to a hydraulic pump via a respective electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine. Each of the cryogenic pumps also has first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber. The method also includes supplying hydraulic fluid under pressure to the hydraulic chamber of each of the plurality of cryogenic pumps via its respective electrohydraulic valve responsive to a signal from a controller. The method further includes, for each of the plurality of cryogenic pumps, pumping the cryogenic fuel from the cryogenic tank to the engine via the second piston the cryogenic chamber responsive to application of pressure of the hydraulic fluid at the first piston in the hydraulic chamber.

In yet another aspect of the disclosure, a system for delivering cryogenic fuel from a cryogenic tank to an engine includes a hydraulic pump coupled to an engine oil reservoir, a first electrohydraulic valve of a plurality of electrohydraulic valves coupled to the hydraulic pump and a first cryogenic pump of a plurality of cryogenic pumps. The first cryogenic pump includes a hydraulic chamber coupled to the first electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine where the first cryogenic pump has a first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber. The system also includes a controller coupled to the first electrohydraulic valve. The controller activates the first electrohydraulic valve in a sequence with the other of the plurality of electrohydraulic valves according to a fuel requirement of the engine, wherein the activation of the first electrohydraulic valve causes delivery of cryogenic fuel to the engine via the first cryogenic pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a cryogenic fuel delivery system according to the current disclosure;

FIG. 2 is a block diagram of another embodiment of a cryogenic fuel delivery system according to the current disclosure;

FIG. 3 is a block diagram of yet another embodiment of a cryogenic fuel delivery system according to the current disclosure;

FIG. 4 is a block diagram of still another embodiment of a cryogenic fuel delivery system according to the current disclosure;

FIG. 5 is a cutaway view of an exemplary cryogenic pump;

FIG. 6 is a block diagram of an exemplary controller for use in the cryogenic fuel delivery system;

FIG. 7 is a flow chart of a method of delivering cryogenic fuels;

FIG. 8 is a chart of fuel pressure vs. pump activation signals;

FIG. 9 is a chart of fuel pressure vs. pump activation signals; and

FIG. 10 is a chart of fuel pressure vs. pump activation signals.

DETAILED DESCRIPTION

Cryogenic fuels are those fuels that are gaseous at room temperature and atmospheric pressure but which are stored at very low temperatures in a liquid state. Liquefied natural gas (LNG) is one example of a popular cryogenic fuel being used in engines as an alternative to gasoline or diesel fuels. As discussed above, several problems have hindered the deployment of cryogenic fuels in many applications, among them proximity to the fuel tank and delivery at a consistent pressure over a wide range of flow rates.

FIG. 1 illustrates a fuel delivery system 100 for delivering cryogenic fuel 101 from a cryogenic fuel tank 102 to an engine 104. The cryogenic fuel tank 102 and the engine 104 are coupled to the system 100 but are not necessarily part of the system 100. The system 100 includes a feed pump 106 for supplying the cryogenic fuel 101 via a feed line 108 to a plurality of cryogenic pumps 118, 119, 120 that are hydraulically operated. The feed pump 106 maintains a high enough pressure in the feed line 108 so that cryogenic fuel 101 remains in a liquefied form even if it's temperature rises slightly while being transported to the cryogenic pumps discussed below. The use of the feed pump 106 allows the system 100 to be separated from the cryogenic fuel tank 102 for use in applications where available space previously prohibited use of cryogenic fuels.

Check valves 110, 111, and 112, prevent the cryogenic fuel 101 from returning to the cryogenic fuel tank 102. The embodiment illustrated in FIG. 1 shows three cryogenic pumps but in practice the number of cryogenic pumps may range from two to nine or more depending on the pressure and delivery rate required for a particular application.

The cryogenic pumps 118, 119, 120 supply cryogenic fuel 101 under pressure to the engine 104 via another set of check valves 114, 115, 116, that prevent back flow of cryogenic fuel 101 output from one pump to another of the cryogenic pumps 118-120.

A plurality of electrohydraulic valves 122, 123, 124 are coupled to respective cryogenic pumps 118, 119, 120 and are configured to selectively supply hydraulic fluid 127 to or drain hydraulic fluid 127 from its respective cryogenic pump 118-120. The hydraulic fluid 127 is supplied to the electrohydraulic valves 122-124 under pressure by a hydraulic pump 126 from an oil reservoir 128 via a hydraulic line 130. In an embodiment, the oil reservoir 128 may be simply a tank for engine lubricating oil so that there is no requirement for a separate hydraulic fluid system simply to drive the electrohydraulic valves 122-124. Alternatively, a separate hydraulic system may be used. In the illustrated embodiment, each representation of an oil reservoir (or tank) is the same oil reservoir 128. An accumulator 132 may be used to store hydraulic fluid 127 under pressure for use in driving the cryogenic pumps 118-120 during times of high demand. A relief valve 133 may protect against potentially damaging high pressures in the hydraulic line 130. Each of the electrohydraulic valves 122-124 connects its respective cryogenic pump 118-120 to either the hydraulic line 130 or its drain line 134, 135, 136.

The electrohydraulic valves 122-124 operate responsive to a signal from a controller 138. The controller 138 may be a comprehensive engine controller with responsibility for as much as all engine, body, and tool or accessory controls or may simply be focused on management of cryogenic fuel delivery, or various combinations between these. The controller 138 may have a separate output for each electrohydraulic valve 122-124 (A, B, C). Based on the fuel demands of the engine 104, the controller 138 may sequentially activate the cryogenic pumps 118-120 with a given duty cycle to provide the necessary pressure, fuel volume, or both. The controller 138 may also include input lines from, for example, the engine 104 as designated by the bus line connection 140. The controller 138 is discussed in more detail below. A typical embodiment of the system of FIG. 1 may include a vaporizer and a gas-side accumulator in line with the engine 104. These components are not depicted for clarity purposes.

In an exemplary embodiment, the electrohydraulic valve 122 and its associated cryogenic pump 118 shown schematically as separate elements in FIG. 1 may be combined into a single unit electrohydraulic (EH) valve-pump unit 142.

FIG. 2 illustrates another embodiment of a cryogenic fuel delivery system 300. The tank return path is not shown in order to emphasize the relevant portions of the figure. The embodiment of FIG. 2 is similar to that of FIG. 1, but each cryogenic pump 318, 319, 320 is coupled to two electro-hydraulic valves. That is, cryogenic pump 318 may be coupled to electro-hydraulic valve 122 and to electro-hydraulic valve 122′. Similarly, cryogenic pumps 319 and 320 have respective electro-hydraulic valves 123/123′ and 124/124′. The controller 338 is modified with additional outputs A′, B′, and C′ in order to provide separate controls for each of the additional electro-hydraulic valves 122′, 123′, and 124′.

The addition of the second electro-hydraulic valve allows increased flow rate into the cryogenic pump in a situation where performance of the system is limited by the capacity of the electro-hydraulic valve 122. For example, a cryogenic pump 318 may have its flow rate doubled by increasing its rate from 200 strokes/minute to 400 strokes/minute through the use of the second electro-hydraulic valve 122′. In addition, the second electro-hydraulic valve for each cryogenic pump provides redundancy should one electro-hydraulic valve fail.

FIG. 3 is a block diagram of another cryogenic fuel delivery system 301. The tank return path is not shown to reduce clutter and emphasize the relevant portions of the figure. The embodiment of FIG. 3 is similar to the embodiment of FIG. 1 in that each cryogenic pump 118, 119, and 120 has a single, respective electro-hydraulic valve 322, 323, 324. In contrast to the embodiment of FIG. 1, this embodiment uses proportional control electro-hydraulic valves. That is, the electro-hydraulic valves 322, 323 and 324 are responsive to an analog or digital control signal input that opens the valve an amount proportional to the analog level of the control signal. This allows finer control of the fuel delivery profile compared to the fully open or fully closed electro-hydraulic valves of FIGS. 1 and 2 because not only the magnitude of the cryogenic pump displacement can be controlled but also the rate of the displacement of the cryogenic pump can be controlled. The controller 339 must be capable of providing the digital or analog outputs over a range that sets the valves 322, 323, and 324 to the desired hydraulic fluid delivery rate.

FIG. 4 is a block diagram of yet another cryogenic fuel delivery system 302. The tank return path is not shown to reduce clutter and emphasize the relevant portions of the figure. The embodiment of FIG. 4 is a combination of the dual electro-hydraulic valve arrangement of FIG. 2 with the proportional control electro-hydraulic valve arrangement of FIG. 3. The controller 340 has outputs for each of the electro-hydraulic valves. Each of the outputs must be capable of providing an analog or digital signal used by the respective valves for setting an opening valve or flow rate. The additional proportional control valves provide an ability to finely control the fuel delivery profile in terms of volume, pressure, and rate over a simpler embodiment such as that of FIG. 1.

FIG. 5 illustrates a cutaway view an embodiment of an EH valve-pump unit 142. The EH valve-pump unit 142 may include a hydraulic fluid inlet 143 coupled to the hydraulic line 130 and a drain 144 coupled to the drain line 134. A spool 146 moves responsive to an electric current being applied to a solenoid 148. The spool 146 connects either a fluid inlet 143 or the drain 144 with a hydraulic chamber 150. A first piston 152 in the hydraulic chamber 150 is coupled to a second piston 154 that is disposed in a cryogenic chamber 156. Cryogenic fuel enters via a first port 158 and is expelled through a second port 160 with the direction set by a check valve (not shown). In other embodiments, a single port 158 may serve both as an inlet and outlet with fuel flow controlled by the external check valves 110 and 114 (FIG. 1).

The first piston 152 and the second piston 154 may be coupled by a shaft 162 so that the first piston 152 and the second piston 154 move in unison. A surface area of the first piston 152 (corresponding to its larger diameter illustrated) is greater than a surface area of the second piston 154 so there is an intensified relationship between the hydraulic pressure against the first piston 152 and the second piston 154 against the cryogenic fuel 101. A spring return 164 moves the first piston 152 back toward the electrohydraulic valve 122 when the spool 146 couples the hydraulic chamber 150 to the drain 144. In other embodiments the return movement of the first piston 152 may be part of another active hydraulic circuit. In either the spring return embodiment or the active hydraulic circuit embodiment or another return strategy, pressurized flow from pump 106 will assist in the retraction of pistons 152 & 154.

During the pumping process a certain portion of the cryogenic fuel 101 may experience an increase in temperature or a pressure drop which may cause a state change to a gaseous form. This gas may move past the seals of the second piston 154 to a shaft side of the cryogenic chamber 166 and may be vented via the gas bleed outlet 168. The gas bleed outlet 168 may be coupled to a recovery system or may simply be vented to the atmosphere. Similarly, a certain amount of hydraulic fluid may escape past the seals of the first piston 152 and may be expelled via port 170 back to the oil reservoir 128.

FIG. 6 illustrates an exemplary controller 138 that may function, among other things to set the duration and timing of cryogenic pumps 118-120 by controlling activation of their respective electrohydraulic valves 122-124 and more specifically, their solenoids 148. The controller 138 may include a processor 200 and a memory 202 coupled by data bus 204. The data bus 204 may also be coupled to an input block 206 with various inputs from, for example, engine sensors, a throttle sensor, transmission or torque converter sensors, etc. for use in determining fuel requirements of the engine 104. The controller 138 may also include a series of output drivers 208, 210, 212, 214 for activating individual electrohydraulic valves that operate respective cryogenic pumps.

The memory 202 may be any of several physical memories, including without limitations combinations of volatile and non-volatile RAM, ROM, flash, PROM, EEPROM or other memory technologies and constructions. The memory 202 is a physical memory and does not include carrier wave or other propagated media transient memories.

The memory 202 may include an operating system 216 and utilities 218 that manage the interactions of the processor 200 for internal and external communication, memory access, programming and diagnostics. The memory 202 may also include an engine strategy 220 that uses data received via the input block 206 to determine settings for various engine parameters such as spark timing and fuel injector timing, among other things. A fuel routine 222 may work in conjunction with other elements of the engine strategy 220 to determine a fuel requirement for the engine 104. The fuel routine 222 may then activate the drivers 208, 210, 212, etc. for the electrohydraulic valves according to the strategy.

While discussing the fuel routine 222, turn briefly to FIGS. 8-10. These figures illustrate but a few of many various pump operation strategies. FIG. 8 is a chart 400 showing ‘digital’ operation of a single pump to deliver a low volume of cryogenic fuel. For low delivery rates, use of the single pump can simplify the control strategy and save wear and tear on the other pumps. As shown, a single pump 118 is operated in pulses so that the piston 154 is selectively advanced according to a displacement line 402. During periods where the piston 118 is advancing, the flow rate line 404 shows that fuel is flowing at a constant rate and when the piston is stopped there is no flow. The average fuel delivered is illustrated by line 406.

FIG. 9 is a chart 410 illustrating non-overlapping operation of three pumps, such as pumps 118, 119, 120. The sawtooth lines 412, 416, and 420 show displacement of each of the three pumps. Corresponding flow rate lines 414, 418, and 422 illustrate the fuel flow rate attributable to each pump. As expected, the linear displacement of a pump provides a constant flow rate from that pump. The total flow rate line 424 is the sum of each individual pump flow rate. (The total flow rate line 424 is shown offset from the individual flow rates for clarity of the illustration.)

FIG. 10 is a chart 440 illustrating overlapping operation of three pumps, such as pumps 118, 119, 120. The sawtooth lines 442 an 446 illustrate the full displacement cycle of their respective pumps. That is, the line 442 shows one pump operating from 0 displacement to full displacement followed by a rapid return stroke back to 0 displacement. The line 450 shows the partial cycle of one pump. The flow rate for each pump is shown by lines 444, 448, and 452. The total fuel being delivered to the engine 104 the sum of each individual pump flow rate as shown by the total flow rate line 454.

INDUSTRIAL APPLICABILITY

FIG. 7 is a flow chart of a method 250 of using a system 100 to deliver cryogenic fuel 101 from a cryogenic fuel tank 102 to an engine 104. At block 252, a plurality of cryogenic pumps 118, 119, 120 are provided as part of a fuel delivery system 100. Each cryogenic pump 118-120 has a hydraulic chamber 150 coupled to a hydraulic pump 126 via a respective electrohydraulic valve 122, 123, 124. Each cryogenic pump 118-120 also has a cryogenic chamber 156 coupled to the cryogenic fuel tank 102 and the engine 104. Each of the cryogenic pumps 118-120 has a first piston 152 in the hydraulic chamber 150 coupled by a shaft 162 to a second piston 154 in the cryogenic chamber 156. In an embodiment, each of the cryogenic pumps 118-120 may be an intensified pump, that is, in each pump, a surface area of the first piston 152 is greater than a surface area of the second piston 154.

At block 254, the controller 138 may activate signals that control flow of pressurized hydraulic fluid to the hydraulic chamber 150 of each of the plurality of cryogenic pumps 118-120. As discussed above, the signals are based on an overall engine strategy to meet the fuel needs of the engine 104. An accumulator 132 may be disposed on a hydraulic line 130 that supplies the hydraulic fluid to each of the plurality of cryogenic pumps 118-120. In an embodiment, the hydraulic fluid is engine lubricating oil so that for each of the plurality of cryogenic pumps 118-120 spent hydraulic fluid is drained from the hydraulic chamber 150 to a reservoir 128 of engine lubricating oil.

At block 256, cryogenic fuel 101 may be supplied to each of the plurality of cryogenic pumps 118-120. In an embodiment, the cryogenic fuel 101 may be supplied under pressure using a feed pump 106.

At block 258, the cryogenic fuel 101 received from the cryogenic fuel tank 102 may be pumped to the engine 104 via the second piston 154 in the cryogenic chamber 156 responsive to application of pressure of the hydraulic fluid at the first piston 152 in the hydraulic chamber 150.

At a block 260, check valves 110, 111, 112 may be used for preventing backflow of cryogenic fuel 101 from any of the plurality of cryogenic pumps 118-120 to the cryogenic fuel tank 102. Check valves 114, 115, 116 may be used for preventing backflow of cryogenic fuel 101 from any of the cryogenic pumps 118-120 to any other of the plurality of cryogenic pumps 118-120.

At block 262, fuel vapor that bypasses the second piston 154 may be bled from a shaft side of the cryogenic chamber 166 via a gas bleed outlet 168. The disclosed fuel delivery system 100 and method provide significant advantages to both manufacturers and users of equipment that can operate on cryogenic fuels. The use of a plurality of cryogenic pumps 118-120 significantly increases the level of control for fuel pressure and delivery rate while reducing fuel pressure ripple. The feed pump 106 maintains pressure in feed lines 108 to keep the cryogenic fuel 101 in a liquid state even if it warms slightly in transit to the cryogenic pumps 118-130. This allows location of the cryogenic pumps 118-120 farther from the cryogenic fuel tank 102 than was previously possible, enabling the use of cryogenic fuels in new applications such as, but not limited to, locomotives and other space restricted applications. The ability to use simple engine lubricating oil to drive the cryogenic pumps simplifies both supply and return paths for the hydraulic actuating fluid and eliminates the need for separate oil systems required by prior art crank and crosshead drives. 

What is claimed is:
 1. A system for delivering cryogenic fuel from a cryogenic fuel tank to an engine, the system comprising: a plurality of cryogenic pumps that are hydraulically operated coupled to the cryogenic tank; a plurality of electrohydraulic valves, each of the plurality of electrohydraulic valves coupled to one respective cryogenic pump of the plurality of cryogenic pumps, each of the plurality of electrohydraulic valves configured to selectively supply or drain a hydraulic fluid to its respective cryogenic pump; and a controller coupled to each of the plurality of electrohydraulic valves, the controller configured to activate each of the plurality of electrohydraulic valves in a sequence according to a fuel requirement of the engine.
 2. The system of claim 1, further comprising a feed pump that maintains pressure in a feed line that couples the cryogenic fuel tank to each of the plurality of cryogenic pumps.
 3. The system of claim 1, further comprising a hydraulic pump that supplies the hydraulic fluid to each of the plurality of electrohydraulic valves.
 4. The system of claim 3, wherein each of the plurality of electrohydraulic valves has a drain that channels the hydraulic fluid from its respective one of the plurality of cryogenic pumps to a reservoir for engine lubricating oil.
 5. The system of claim 3, wherein the one of the plurality of cryogenic pumps and one of the plurality of electrohydraulic valves are combined into a single electrohydraulic (EH) valve-pump unit.
 6. The system of claim 1, wherein each of the plurality of cryogenic pumps is an intensified pump wherein an first area of a first piston in contact with the hydraulic fluid is greater than a second area of a second piston in contact with the cryogenic fuel.
 7. The system of claim 1, further comprising a first check valve disposed in a feed line coupling the cryogenic tank to the each of the plurality of cryogenic pumps, the first check valve configured to prevent cryogenic fuel output from any of the plurality of cryogenic pumps from returning to the fuel tank, and a second check valve that prevents flow of the cryogenic fuel from any of the plurality of cryogenic pumps to another of the plurality of cryogenic pumps.
 8. The system of claim 1, wherein each of the plurality of cryogenic pumps has a hydraulic chamber with a first piston and a cryogenic chamber with a second piston, the first and second pistons coupled by a shaft, the cryogenic chamber having a gas bleed outlet on a shaft-side of the second piston.
 9. The system of claim 1, wherein the plurality of cryogenic pumps has three cryogenic pumps.
 10. A method of delivering a cryogenic fuel from a cryogenic tank to an engine, the method comprising: providing a plurality of cryogenic pumps, each cryogenic pump having a hydraulic chamber coupled to a hydraulic pump via a respective electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine, each of the cryogenic pumps having a first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber; supplying a hydraulic fluid under pressure to the hydraulic chamber of each of the plurality of cryogenic pumps via its respective electrohydraulic valve responsive to a signal from a controller; and for each of the plurality of cryogenic pumps, pumping the cryogenic fuel from the cryogenic tank to the engine via the second piston of the cryogenic chamber responsive to application of pressure of the hydraulic fluid at the first piston in the hydraulic chamber.
 11. The method of claim 10, further comprising supplying cryogenic fuel under pressure to each of the plurality of cryogenic pumps using a feed pump.
 12. The method of claim 10, further comprising: for each of the plurality of cryogenic pumps, draining the hydraulic fluid from the hydraulic chamber to a reservoir for engine lubricating oil.
 13. The method of claim 10, wherein supplying hydraulic fluid under pressure comprises disposing an accumulator between the hydraulic pump and each of the plurality of cryogenic pumps.
 14. The method of claim 10, wherein for each of the plurality of cryogenic pumps, a surface area of each first piston is greater than a surface area of each second piston.
 15. The method of claim 10, further comprising: preventing backflow of cryogenic fuel from any of the plurality of cryogenic pumps to the cryogenic tank; and preventing backflow of cryogenic fuel from any of the cryogenic pumps to any other of the plurality of cryogenic pumps.
 16. The method of claim 10, further comprising: bleeding fuel vapor that bypasses the second piston from a shaft-side of the cryogenic chamber.
 17. A system for delivering cryogenic fuel from a cryogenic fuel tank to an engine comprising: a hydraulic pump coupled to an engine oil reservoir; a first electrohydraulic valve of a plurality of electrohydraulic valves coupled to the hydraulic pump; a first cryogenic pump of a plurality of cryogenic pumps, the first cryogenic pump including a hydraulic chamber coupled to the first electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine, the first cryogenic pump having a first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber; and a controller coupled to the first electrohydraulic valve, the controller configured to activate the first electrohydraulic valve in a sequence with the other of the plurality of electrohydraulic valves according to a fuel requirement of the engine, wherein the activation of the first electrohydraulic valve causes delivery of the cryogenic fuel to the engine via the first cryogenic pump.
 18. The system of claim 17, further comprising a feed pump that maintains pressure in a feed line that couples the cryogenic fuel tank to each of the plurality of cryogenic pumps.
 19. The system of claim 17, wherein the first electrohydraulic valve has a drain that channels hydraulic fluid from first cryogenic pumps to a reservoir for engine lubricating oil.
 20. The system of claim 17, wherein the cryogenic chamber has a pump-side and a shaft-side relative to the second piston, the shaft side including a gas bleed outlet that vents vaporized fuel that escapes around the second piston from the pump side to the shaft side. 